German beaten by Japanese teenager Osaka after Czech world No 1 beats Poland's 72nd-ranked Magda Linette 6-2, 6-1.
US Open, Day 2: Kerber latest top seed to crash out but Pliskova reaches second round
Japanese teenager Naomi Osaka sent defending champion Angelique Kerber crashing out of the US Open first round on Tuesday, bringing a rare bright spot to a rain-lashed day at Flushing Meadows.
As players ran for cover off the outside courts, Osaka's big-hitting game and love of the big occasion thrived under the roof of the Arthur Ashe Stadium court.
The world No 46, born in Japan to a Haitian father and Japanese mother, won 6-3, 6-1 as sixth seed Kerber became the first US Open women's defending champion to lose in the first round since Svetlana Kuznetsova in 2005.
Osaka, who surrendered a 5-1 third set lead on the same court in losing to Madison Keys 12 months ago, fired 22 winners as Kerber went tumbling out of the world's top 10 as well as the tournament.
"At 4-1, I was hoping I don't do what I did last year," said the 19-year-old Osaka, who conceded suffering a brief flashback to her tearful loss to Keys.
"So that helped me focus and concentrate, which I needed as Angelique gets everything back."
Osaka will face either Sweden's Rebecca Peterson or Denisa Allertova of the Czech Republic for a place in the last 32.
"I just want to play good. I did that today and so I want to carry that into the next match," added the Japanese teenager, who secured her first career win over a top-10 player.
Kerber is the third top seed to go out in the first round after No 2 Simona Halep and seventh-seeded Johanna Konta lost on Monday.
World No 1 Karolina Pliskova, bidding to back up her lofty status with a first grand slam title, also made a winning start.
Czech 25-year-old Pliskova, the runner-up in 2016, eased past Poland's Magda Linette 6-2, 6-1 on the back of eight aces and 29 winners.
"I felt a little bit nervous walking on this court, especially after last year and the memories I have here," said Pliskova, whose progression to the second round was only briefly halted by the roof on Arthur Ashe stadium being closed.